Conjugated polymers are organic macromolecules comprising at least one backbone chain of alternating double- and single-bonds. The opto-electronic properties of conjugated (semi-conducting) polymers have created opportunities for a number of applications such as, for example, light-emitting diodes, light-emitting electrochemical cells, solid-state lasers, solar cells, photodetectors and recently biological and chemical sensors for use in medical diagnostics and toxicology.
It is essential for active layers in chemo- or bio-sensors to combine two functions, i.e., selective molecular recognition and signal transduction. Molecular imprinting polymers (MIP) have unique properties that make them especially suitable for this sensor technology. MIPs exhibit a good specificity to various compounds of medical, environmental, and industrial interest and have excellent operational stability. However, because these arrangements do not fulfill the criterion that a biosensor has a recognition element and transducer in close proximity, they cannot be considered biomimetic sensors in the strict sense.
Bio-electronics is a rapidly progressing interdisciplinary research field at the junction of chemistry, biochemistry, physics, and material science that aims to integrate biomolecules and electronic elements into functional systems. The passage of electrons between biomolecules and electronic elements is the essence of all bio-electronic systems. Nevertheless, electronic units and biomolecules lack natural communication. Different electronic methods have been employed to transduce the biological functions occurring at the electronic supports. These include electrical transduction, such as current, potential changes, piezoelectric transduction, field effect transistors transduction, photo-electrochemical transduction and others.
An important aspect in the design of a MIP-based sensor is to find an appropriate way of interfacing the polymer with the transducer. In most cases, the MIP has to be brought into close contact with the transducer surface. Up to now several approaches were investigated: in situ electro-polymerization on conducting surfaces such as gold; entrapped MIP-particles into gels and behind a membrane for use with electrochemical transducers; spin-coated suspension of MIP particles in solution of inert PVC polymer; and composite particles consisting of an electrically grown conducting polypyrrole into a preformed porous MIP.
Up to now grafting of molecularly imprinted polymers or MIPs was reported as grafted coatings on various porous or non-porous surface supports, inorganic materials as oxide or silica particles, on organic materials as resins, i.e., non-conducting materials.
WO 01/19886 provides a material that consists of a support coated with a polymer and a method for forming it. The material is prepared by grafting a polymer layer on the surface of a performed organic or inorganic support material or surface. The grafting can be combined with the technique of molecular imprinting. A molecularly imprinted polymer can be obtained by polymerizing a composition comprising at least one monomer, and a template on a support in a polymerization medium with a free radical initiator, whereafter the template is removed from the resultant polymer. The polymerization is confined on the surface of the support. The support used in the preferred embodiments is preferably selected from the group consisting of porous and non-porous, planar and non-planar inorganic and organic supports. As examples of such support materials can be mentioned oxides such as alumina and silica, and organic resins.
The main drawback of MIPs for use in sensors is the fact that they do not have transducer properties. Hence, they can not convert biological signals into optical or electrical signals, which is a key feature for sensors which are to be used in, for example, molecular diagnostics, and biological or chemical sample analysis.